1. Field of the Invention
The present invention concerns a vacuum arc evaporation method which is applied when a wearing resistant film or the like is formed, for example, on the surface of tools or dies.
2. Prior Art Statement
In tools or dies, performance such as cutting property or durability can be increased by coating a wearing resistant hard film, for example, comprising TiN. An example of a vacuum arc evaporation device for use in formation of such films is disclosed in laid-open technical publication No. 93-8299 issued by Hatsumei Kyokai. The constitution of the device is explained with reference to FIG. 2 as an explanatory view for the present invention. The device has a vacuum chamber 1 in which a film forming chamber 3 having a substrate 2 (for example, a tool) disposed therein and an ion generation chamber 5 having a vacuum arc evaporation source 9 comprising a Ti target or the like disposed therein are connected with each other by way of a tubular portion 4.
In this device, the evaporation source 9 is locally evaporated and further converted into plasmas by generating an arc spot on the surface of a vacuum arc evaporation source 9, that is, an arc evaporation surface 9a. A TiN film is formed on the surface of the substrate 2 by introducing positive ions in the plasmas to the substrate 2 and supplying a nitrogen gas into the vacuum chamber 1 for reaction. For introducing the positive ions to the substrate 2, an air-core coil 10 is wound around the outer circumference of the tubular portion 4 for forming magnetic fields from the arc evaporation surface 9a to the substrate 2. Further, a negative bias voltage is applied to the substrate 2.
It should be noted that before forming the film to the surface of the substrate 2 as described above, the substrate 2 is cleaned by ion bombardment. This has been conducted by supplying an argon gas into the vacuum chamber 1 and increasing a negative voltage applied to the substrate 2 higher than that upon film formation. In this case, the argon gas is also ionized by the arc discharge in the ion generation chamber 5, which is introduced to the surface of the substrate 2 and further accelerated by an electric field in the periphery of the substrate applied with the high negative voltage and caused to collide against the substrate 2. This sputters the surface of the substrate 2 and removes contamination or the like on the surface to clean up the substrate. By applying the cleaning as described above, adhesion between the film to be formed subsequently and the substrate 2 is improved.
The arc spot described above moves at a high speed on the arc evaporation surface 9a. From the arc spot, electrons and vapors of materials, as well as molten particles (macro particles) are scattered. If the molten particles are deposited to the substrate 2 during cleaning, the surface roughness of the film layer formed subsequently is deteriorated.
Then, for reducing the deposition of the molten particles on the substrate 2, magnetic fields are formed between the ion generation chamber 5 and the film forming chamber 3 by the air-core coil 10 in the device described above and the ions are introduced to the substrate 2 by the magnetic fields. That is, no induction effects by the magnetic fields exert on the neutral molten particles, thus molten particles reaching and depositing on the substrate 2 are reduced.
Further, the magnetic fields described above are determined such that they have a component in parallel with the surface on the arc evaporation surface 9a, that is, a component is perpendicular to ions or electrons flowing out of the arc spot. This also causes an effect of compulsorily moving the arc spot by electromagnetic inter-repulsing action, and the arc spot moves on the arc evaporation surface 9a at a higher speed. As a result, the staying time of the arc spot at one position is shortened to reduce a molten region at the periphery of the arc spot and the amount of the molten particles generated from the arc evaporation surface 9a is also decreased. As described above, the reduction of the surface roughness caused by the molten particles can be suppressed to some extent by the combined use of magnetic field effects.
However, also in the device as described above, although the adhesion between the film and the substrate 2 is increased by the existent cleaning method described above, the surface roughness is still deteriorated due to the molten particles deposited on the surface of the film, so that it leaves a problem that a film having satisfactory characteristic cannot be formed.